Oxidation of chlorinated ethenes by potassium permanganate: a kinetics study.

The kinetics of oxidation of perchloroethylene (PCE), trichloroethylene (TCE), three isomers of dichloroethylene (DCE) and vinyl chloride (VC) by potassium permanganate (KMnO(4)) were studied in phosphate-buffered solutions of pH 7 and ionic strength approximately 0.05 M and under isothermal, completely mixed and zero headspace conditions. Experimental results have shown that the reaction appears to be second order overall and first order individually with respect to both KMnO(4) and all chlorinated ethenes (CEs), except VC. The degradation of VC by KMnO(4) is a two-consecutive-step process. The second step, being the rate-limiting step, is of first order in VC and has an activation energy (E(a)) of 7.9+/-1 kcal mol(-1). The second order rate constants at 20 degrees C are 0.035+/-0.004 M(-1) s(-1) (PCE), 0.80+/-0.12 M(-1) s(-1) (TCE), 1.52+/-0.05 M(-1) s(-1) (cis-DCE), 2.1+/-0.2 M(-1) s(-1) (1,1-DCE) and 48.6+/-0.9 M(-1) s(-1) (trans-DCE). The E(a) and entropy (DeltaS(*)) of the reaction between KMnO(4) and CEs (except VC) are in the range of 5.8-9.3 kcal mol(-1) and -33 to -36 kcal mol(-1) K(-1), respectively. Moreover, KMnO(4) is able to completely dechlorinate CEs, and the increase in acidity of the solution due to CE oxidation by KMnO(4) is directly proportional to the number of chlorine atoms in CEs.

The mechanism and applicability of in situ oxidation of trichloroethylene with Fenton's reagent.

Fenton's reagent is the result of reaction between hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)), producing the hydroxyl radical (-*OH). The hydroxyl radical is a strong oxidant capable of oxidizing various organic compounds. The mechanism of oxidizing trichloroethylene (TCE) in groundwater and soil slurries with Fenton's reagent and the feasibility of injecting Fenton's reagent into a sandy aquifer were examined with bench-scale soil column and batch experiment studies. Under batch experimental conditions and low pH values ( approximately 3), Fenton's reagent was able to oxidize 93-100% (by weight) of dissolved TCE in groundwater and 98-102% (by weight) of TCE in soil slurries. Hydrogen peroxide decomposed rapidly in the test soil medium in both batch and column experiments. Due to competition between H(2)O(2) and TCE for hydroxyl radicals in the aqueous solutions and soil slurries, the presence of TCE significantly decreased the degradation rate of H(2)O(2) and was preferentially degraded by hydroxyl radicals. In the batch experiments, Fenton's reagent was able to completely dechlorinate the aqueous-phase TCE with and without the presence of soil and no VOC intermediates or by-products were found in the oxidation process. In the soil column experiments, it was found that application of high concentrations of H(2)O(2) with addition of no Fe(2+) generated large quantities of gas in a short period of time, sparging about 70% of the dissolved TCE into the gaseous phase with little or no detectable oxidation taking place. Fenton's reagent completely oxidized the dissolved phase TCE in the soil column experiment when TCE and Fenton's regent were simultaneously fed into the column. The results of this study showed that the feasibility of injecting Fenton's reagent or H(2)O(2) as a Fenton-type oxidant into the subsurface is highly dependent on the soil oxidant demand (SOD), presence of sufficient quantities of ferrous iron in the application area, and the proximity of the injection area to the zone of high aqueous concentration of the target contaminant. Also, it was found that in situ application of H(2)O(2) could have a gas-sparging effect on the dissolved VOC in groundwater, requiring careful attention to the remedial system design.